The present invention relates to an electrophotographic copying machine and, more particularly, to an automatic duplex electrophotographic copying machine.
An electrophotographic copying machine produces onto a photoreceptor an electrostatic latent image corresponding to an image of a document such as a manuscript or book to be copied. Toner particles are electrostatically adhered to the latent image, so that the latent image becomes visible as a toner image. The toner image on the photoreceptor is transferred onto a copy paper via a transference charger. The remaining toner particles and charges on the photoreceptor after the transfer arae removed for the next copying operation.
There is present an improved electrophotographic copying machine of the type in which the images on two sheets of documents can be copied onto both sides of one or more copy papers, which is referred to herein as a "duplex copying machine". In such a machine, after the image of a sheet of document has been copied on a single side of a copy paper, the copy paper is turned over to be transported toward the toner image transfer portion, so that the next image is copied onto the other side of the single-side copied paper.
More specifically, in order to realize the above mentioned automatic duplex electrophotographic copying function, the machine involves switch-back means to reverse the travel direction of a single-side copied paper and transport means to convey the reversed single-side copied paper back to the toner image transfer portion. In a conventional copying machine with an automatic duplex copying function, the switch-back means are provided within the machine main body near the copy paper outlet and the transport means under the main paper passage so that a single-side copied paper is turned over within the machine main body to be transported back to the toner image transfer portion. Consequently, the conventional copying machine incorporates therewithin an intricate mechanism related to automatic duplex copying function and, therefore, is of large size. Moreover, the machine has a quite different construction compared with a copying machine with no automatic duplex copying function and, therefore, needs to be produced on a different production line from that for producing the type with no automatic duplex copying function. This results in cost rise. Furthermore, because of the difference in construction as described above, it is not possible to add the automatic duplex copying feature as an option to the copying machine with no automatic duplex copying function. Namely, it is not possible to add automatic duplex copying feature to an ordinary single-side copying machine.